Semiconductors have been widely used for electronic equipment, communication apparatuses and personal computers. High integration, high functionalization and high-density packaging of semiconductors have been in progress. The speed of the progress has been more and more accelerated. In particular, the technology of mobile devices typified by mobile phones has rapidly advanced in recent years. Technological innovation toward the realization of a ubiquitous-computing society is remarkable.
Semiconductor packages unfold from QFP to area mounting type semiconductor packages such as BGA and CSP. In addition, high-functional semiconductor packages such as MCP and SIP appear. Thus the form of semiconductor packages is becoming various. Therefore, laminates for semiconductor packages are more strongly required to have heat resistance, high stiffness, low thermal expansibility, low water absorption properties and other properties.
Conventionally, FR-4 type laminates obtainable by curing epoxy resins with dicyandiamide are widely used as laminates for printed wiring boards. However, this technology cannot sufficiently cope with a demand for high heat resistance. Cyanate ester resins are known as highly-heat-resistant resins for printed wiring boards. Compositions comprising, as a base composition, resin compositions containing bisphenol A type cyanate ester resins and different thermosetting resins or thermoplastic resins are widely used for laminates for semiconductor packages in recent years.
The above-mentioned bisphenol A type cyanate ester resins have excellent properties in terms of electrical characteristics, mechanical properties, resistance to chemical and adhesive properties. However, the bisphenol A type cyanate ester resins are insufficient under severe conditions from the viewpoint of water absorption properties or heat resistance after moisture absorption in some cases. Therefore, cyanate ester resins having different structures have been studied with the aim of further improvement in properties.
As the cyanate ester resins having different structures, novolak type cyanate ester resins are used in many cases (see, for example, JP-A-11-124433). The novolak type cyanate ester resins are apt to be insufficient in curing degree under normal curing conditions, and cured products obtained therefrom have problems such as a high water absorption coefficient and a decrease in heat resistance after moisture absorption. Prepolymers of the novolak type cyanate ester resins with bisphenol A type cyanate ester resins are disclosed as a technology for improving the novolak type cyanate ester resins (see, for example, JP-A-2000-191776). Although the above prepolymers are improved in curability, the prepolymers are not sufficient in view of improvement in other properties. Further, the use of naphthol aralkyl type cyanate esters has been studied (see, for example, JP-A-2006-193607). The naphthol aralkyl type cyanate esters retain heat resistance owing to their stiff resin skeleton structure. In addition, their curability is increased by decreasing reaction inhibition factors. Thus, resin compositions having a low water absorption coefficient and excellent heat resistance after moisture absorption are obtained.
Further, it is normally necessary for laminates for printed wiring boards for use in electronic equipment to have flame resistance. Conventionally, a bromine-containing flame retardant is jointly used for the purpose of imparting flame resistance (see, for example, JP-A-11-021452). However, resin compositions containing no halogen compound are desired in accordance with a recent growing interest in environmental issues. Phosphorus compounds have been studied as a nonhalogen flame retardant. However, there is a danger that a toxic compound such as phosphine generates at the time of combustion. Silicone-containing flame retardants and metal hydrates are known as other flame retardants. The use of a silicone-containing flame retardant as flame retardant has been also studied (see, for example, JP-A-2006-348187). However, a different flame retardant is required for obtaining high flame resistance. Aluminum hydroxide or the like is known as the metal hydrate. It is known that aluminum hydroxide discharges crystal water at the time of heating and, owing to this reaction, works as a flame retardant. However, when a metal hydrate such as aluminum hydroxide is singly used as a flame retardant, it is necessary in many cases to incorporate the metal hydrate in an amount of 50 wt % or more for attaining UL94V-0 (see, for example, JP-A-2001-226465). When gibbsite, which is a general structure of aluminum hydroxide, is added in a large amount, resistance to chemical such as alkali or acid is apt to be extremely poor. An etching treatment, a desmearing treatment, a plating treatment and the like are carried out in the steps of producing printed wiring boards and these treatments are conducted under severe alkaline or acid conditions. Therefore, it is required to improve an insulating layer which is poor in resistance to chemical.
Further, in the assembly process of semiconductor packages, thermal processing is carried out at 120 to 200° C. in steps of baking, wire-bonding, die attachment, mold resin curing, etc. Lead-free solder is used instead of conventional lead solder in solder ball connection from the viewpoint of environmental issues so that a reflow temperature is increased by 20 to 30° C. Therefore, it is endlessly required that laminates for semiconductor packages have higher heat resistance. Since the dehydration starting temperature of gibbsite is slightly higher than 200° C., laminates using gibbsite as a flame retardant are poor in heat resistance in processing at a high temperature of more than 200° C. in some cases. With regard to laminates, which are required to have high reliability, for semiconductor packages, development of laminates having excellent heat resistance and comprising no halogen compound is desired.
It is required that laminate materials for high-performance printed wiring boards used for semiconductor packages have many properties mentioned above. There are technologies which separately improve individual properties. However, there is a strong demand for a material which has all of the required properties in highly good balance.